/*
 * Copyright 2008 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Text;
using ZXing.Common;

namespace ZXing.OneD
{
   /// <summary>
   /// <p>Implements decoding of the UPC-E format.</p>
   /// <p/>
   /// <p><a href="http://www.barcodeisland.com/upce.phtml">This</a>is a great reference for
   /// UPC-E information.</p>
   ///
   /// <author>Sean Owen</author>
   /// </summary>
   public sealed class UPCEReader : UPCEANReader
   {
      /// <summary>
      /// The pattern that marks the middle, and end, of a UPC-E pattern.
      /// There is no "second half" to a UPC-E barcode.
      /// </summary>
      private static readonly int[] MIDDLE_END_PATTERN = { 1, 1, 1, 1, 1, 1 };

      /// <summary>
      /// See L_AND_G_PATTERNS these values similarly represent patterns of
      /// even-odd parity encodings of digits that imply both the number system (0 or 1)
      /// used, and the check digit.
      /// </summary>
      private static readonly int[][] NUMSYS_AND_CHECK_DIGIT_PATTERNS = {
                                                                  new[] { 0x38, 0x34, 0x32, 0x31, 0x2C, 0x26, 0x23, 0x2A, 0x29, 0x25 },
                                                                  new[] { 0x07, 0x0B, 0x0D, 0x0E, 0x13, 0x19, 0x1C, 0x15, 0x16, 0x1A }
                                                               };

      private readonly int[] decodeMiddleCounters;

      public UPCEReader()
      {
         decodeMiddleCounters = new int[4];
      }

      override internal protected int decodeMiddle(BitArray row, int[] startRange, StringBuilder result)
      {
         int[] counters = decodeMiddleCounters;
         counters[0] = 0;
         counters[1] = 0;
         counters[2] = 0;
         counters[3] = 0;
         int end = row.Size;
         int rowOffset = startRange[1];

         int lgPatternFound = 0;

         for (int x = 0; x < 6 && rowOffset < end; x++)
         {
            int bestMatch;
            if (!decodeDigit(row, counters, rowOffset, L_AND_G_PATTERNS, out bestMatch))
               return -1;
            result.Append((char)('0' + bestMatch % 10));
            foreach (int counter in counters)
            {
               rowOffset += counter;
            }
            if (bestMatch >= 10)
            {
               lgPatternFound |= 1 << (5 - x);
            }
         }

         if (!determineNumSysAndCheckDigit(result, lgPatternFound))
            return -1;

         return rowOffset;
      }

      override protected int[] decodeEnd(BitArray row, int endStart)
      {
         return findGuardPattern(row, endStart, true, MIDDLE_END_PATTERN);
      }

      override protected bool checkChecksum(String s)
      {
         return base.checkChecksum(convertUPCEtoUPCA(s));
      }

      private static bool determineNumSysAndCheckDigit(StringBuilder resultString, int lgPatternFound)
      {

         for (int numSys = 0; numSys <= 1; numSys++)
         {
            for (int d = 0; d < 10; d++)
            {
               if (lgPatternFound == NUMSYS_AND_CHECK_DIGIT_PATTERNS[numSys][d])
               {
                  resultString.Insert(0, new[] { (char)('0' + numSys) });
                  resultString.Append((char)('0' + d));
                  return true;
               }
            }
         }
         return false;
      }

      override internal BarcodeFormat BarcodeFormat
      {
         get { return BarcodeFormat.UPC_E; }
      }

      /// <summary>
      /// Expands a UPC-E value back into its full, equivalent UPC-A code value.
      ///
      /// <param name="upce">UPC-E code as string of digits</param>
      /// <returns>equivalent UPC-A code as string of digits</returns>
      /// </summary>
      public static String convertUPCEtoUPCA(String upce)
      {
         var upceChars = upce.Substring(1, 6);
         StringBuilder result = new StringBuilder(12);
         result.Append(upce[0]);
         char lastChar = upceChars[5];
         switch (lastChar)
         {
            case '0':
            case '1':
            case '2':
               result.Append(upceChars, 0, 2);
               result.Append(lastChar);
               result.Append("0000");
               result.Append(upceChars, 2, 3);
               break;
            case '3':
               result.Append(upceChars, 0, 3);
               result.Append("00000");
               result.Append(upceChars, 3, 2);
               break;
            case '4':
               result.Append(upceChars, 0, 4);
               result.Append("00000");
               result.Append(upceChars[4]);
               break;
            default:
               result.Append(upceChars, 0, 5);
               result.Append("0000");
               result.Append(lastChar);
               break;
         }
         result.Append(upce[7]);
         return result.ToString();
      }

   }
}
